The present invention generally relates to video signal processing systems, and more particularly to a video signal processing system for application in a signal processing system which carries out a pre-emphasis in a recording system which records a video signal onto a recording medium and carries out a de-emphasis in a reproducing system which reproduces the recorded signal from the recording medium. The signal processing system according to the present invention can suppress the overshoot level of an output signal of a pre-emphasis circuit to a relatively low level, and it is unnecessary to greatly clip the output signal level of the pre-emphasis circuit.
Generally in a video signal processing system which carries out a pre-emphasis with respect to the signal in the recording system and carries out a de-emphasis in the reproducing system, the input video signal which is to be recorded is first supplied to a pre-emphasis circuit in the recording system in order to emphasize the high frequency component of the input video signal. The output signal of the pre-emphasis circuit is supplied to a clipping circuit wherein the signal level is clipped so that the level at the tip end of the overshoot in the signal does not exceed a predetermined level. The output signal of the clipping circuit is supplied to a frequency modulating circuit wherein a carrier is frequency modulated by this signal. The output frequency modulated video signal of the frequency modulating circuit, is recorded onto a magnetic tape by a magnetic head. In the reproducing system, the signal which is reproduced from the magnetic tape by the magnetic head, is supplied to a frequency demodulating circuit wherein the reproduced signal is demodulated. The demodulated output of the frequency demodulating circuit is supplied to a de-emphasis circuit wherein the high frequency component which was emphasized in the pre-emphasis circuit in the recording system is de-emphasized or attenuated, to restore the video signal into its original form. The output signal of the de-emphasis circuit is obtained as the reproduced video signal.
As is well known, the signal-to-noise (S/N) ratio becomes deteriorated with respect to the higher frequency components of the frequency modulated video signal by recording and reproducing of the signal. Thus, the S/N ratio in the high frequencies can be improved, by emphasizing the level of the high frequency component in the pre-emphasis circuit as described above, and increasing the modulation factor with respect to the high frequencies.
The conventional pre-emphasis circuit was designed to attenuate the low frequency component with respect to the high frequency component of the input video signal, by use of a filter comprising a capacitor and resistors. On the other hand, the conventional de-emphasis circuit was designed to suppress the high frequency component of the input video signal more than the low frequency component, by use of a filter comprising a capacitor and resistors. These conventional pre-emphasis and de-emphasis circuits each using the filter comprising the capacitor and resistors, can be considered as a circuit which performs weighting with respect to an information which was obtained prior to a present information and adds this weighted information to the present information. In the present specification, a type of circuit which performs weighting with respect to the information which was obtained prior to the present information and adds this weighted information to the present information in this manner, will be referred to as a "forward type" circuit.
As a forward type filter other than the above filters comprising the capacitor and resistors, there was a forward type transversal filter comprising a plurality of delay circuits, a plurality of coefficient multipliers, and an adder.
However, according to the conventional pre-emphasis circuit employing any of the above filters, a large overshoot is introduced at the rising and falling portions of the pre-emphasized signal waveform if a square wave signal is subjected to the pre-emphasis. When a large overshoot which exceeds a certain level exists in the pre-emphasized signal, a so-called inversion phenomenon occurs if a frequency modulated video signal which is obtained by frequency modulating a carrier by this pre-emphasized signal is recorded onto and reproduced from the magnetic tape. The inversion phenomenon is the phenomenon in which the black and white at parts of the reproduced picture which correspond to the overshoots become inverted. Accordingly, in order to prevent this inversion phenomenon from occurring, a clipping circuit was provided between the pre-emphasis circuit and the frequency modulating circuit in the conventional circuit. This clipping circuit clipped the signal level so that the level at the tip end of the overshoot in the signal does not exceed a predetermined level.
However, if the clipping circuit greatly clips the overshoot of the pre-emphasized signal so as to prevent the inversion phenomenon from occurring, the picture quality of the reproduced picture deteriorates at parts which correspond to the overshoots which have been greatly clipped.